The present invention relates generally to document handling systems, and more particularly to a novel method and apparatus for shingling a stack of documents as they are fed toward a singulating station.
It is a common practice in the automated handling of documents, such as mailing envelopes and flats, to progressively feed a stack of documents in a feeder station or magazine to a singulating station from which the documents are fed as separated single documents to a sorting station or other processing station. To better prepare the stacked documents for singulating, means are conventionally provided to shingle the documents prior to their entering the singulating station. Shingling results in orienting either the top or bottom document in a vertical stack, or the front or lead document in an on-edge stack, so that the forward or leading edge of each successive top, bottom or front document is disposed slightly forwardly or laterally of the leading edge of the next adjacent document, preferably by a distance of approximately one inch. By shingling the stacked documents, only one document at a time will enter the nip defined by singulating belts or rollers, thereby substantially reducing the possibility that more than one document at a time will be fed simultaneously through the singulating belts or rollers.
Prior techniques for shingling on-edge stacked documents include passive shingling wherein a triangular shaped plate is disposed over a flat feed belt disposed transverse to the feed direction of the stack of on-edge documents so that each document is exposed to progressively greater belt contact as the document is fed toward the singulating station. The increasing belt contact applies a progressively greater friction force to the lower edge of each successive document so that each document is advanced or shingled relative to the next successive document in the direction of movement of the transverse belt.
A prior technique for shingling a stack of generally horizontally disposed vertically stacked or face-up documents employs a series of rollers disposed transverse to the feed direction of the stack. The rollers rotate at progressively increasing rotational speeds which causes the lowermost document to be accelerated and advanced relative to the next above document in the stack. A drawback to this technique is that the transverse rollers engage a flat lower surface of the lowermost document and effectively drive one document at a time. Also, the driving force created by the rollers is dependent upon the weight of the stack and the coefficient of friction between the stacked documents.
A variation to differentially driven roller type shinglers is to vibrate the rollers while they are driven at substantially the same rotational speeds so as to create a jogging and jerky acceleration action on the stack. This causes the upper documents in the stack to fall back and thereby create a shingled relation between adjacent documents.
Another prior technique for shingling a stack of documents employs suction or vacuum means to advance each successive document in a vertical or on-edge stack into the nip of a belt or roller type singulating station. A significant disadvantage of suction or vacuum type shingling mechanisms is that they are particularly sensitive to the thickness and relative stiffness of the documents. Also, depending on the porosity of the documents, more than one document at a time may be advanced or shingled relative to the remaining documents. This results in more than one document at a time being fed into the nip of the singulating belts or rollers.
Another prior document shingling technique which finds particular application with on-edge stacks of documents is the use of in-line spiral feeders having variable pitch to separate the leading document or a small group of documents from the rest of the stack. The separated document or small grouping of documents may then be lightly fed against a transverse feed belt capable of moving each successive lead document in shingled relation laterally into the nip of a singulator station which forwards the documents in singulated fashion. Again, however, this technique may result in more than one document at a time being fed simultaneously into the singulating station in nonshingled relation.
Thus, a shingling method and apparatus which significantly increases the efficiency of shingling a stack of on-edge documents so that the leading edge of a single document at a time is introduced into the nip of singulating rollers or belts would greatly improve the rate at which documents could be handled in a document handling system.